1. Technical Field
The present invention relates generally to semiconductor processing, and more particularly, to a method and structure used to fill apertures in high performance electronic substrates.
2. Related Art
In circuit board construction, solder ball connection of a module, such as a ceramic module, provides significant electrical performance advantage over conventional pin-in-hole technology. Pin-in-hole technology involves the attachment of modules to circuit boards using projections or pins which insert into corresponding holes in the board.
Pin-in-hole connections, due to mechanical considerations, occupy considerable surface area of the circuit board thwarting further miniaturization. In contrast, solder ball technology attaches modules to the board using balls of solder on the module which are joined to corresponding contact points on the surface of the board.
Specifically, a high melting point solder ball is placed on the backside of a module and attached to the module with a low melting point solder paste reflow process. The module is then attached to the surface of the circuit board with a screened, low melting point solder paste. Since attachment of the module to the board is made only on the surface of the board, the attachment land drill diameter, and clearance land sizes may be reduced in size, thus allowing greater wiring area. Solder ball connection provides the advantage of enhanced system speed because the signal net length is reduced and also provides the advantage of enhanced wiring capability due to reduced via and land diameters.
However, a problem with solder ball connect technology occurs where the solder ball connection is being made to a conventional through hole or via. When such a connection has been attempted, the screened eutectic paste used to connect the solder ball to the board flows through the hole away from the intended inter-connection site during the reflowing process. This results in poor and unreliable solder joints. One attempt to attach a module directly to a via in pad type of land was to pre-fill the through holes with solder to create a solid land prior to attachment of the solder ball. However, the solder is pulled down through the hole, away from the interconnection during the assembly of the circuit board. This pulling down or xe2x80x9cwickingxe2x80x9d of the solder results in a void below the ball which leads to cracking and thus produces poor, unreliable solder joints.
Another solution to the problem of connecting solder balls to through holes has been to utilize a xe2x80x9cdog-bonexe2x80x9d type termination where a solid copper land is displaced from the plated through hole or via. The solder joint is made to the solid copper land which is then connected by a circuit line to the via or through hole. While the dog bone termination provides excellent solder joints, it decreases the advantages otherwise obtained with the via in pad solder ball connection technology because the wireability is reduced and the signal line length is increased. Concomitantly, the circuit line occupies space or xe2x80x9creal estatexe2x80x9d on the surface of the circuit board.
Attempts have also been made to fill vias and through holes with certain polymer materials, but such polymer materials incompletely fill the vias thereby creating significant voids. Such polymer materials also require lengthy processing time due to drying of the solvent. These polymer materials also tend to shrink as the solvent is released, thus causing non-planar surfaces and additional voids.
It would be desirable to have solder ball connections directly at through holes thereby consuming less real estate, decreasing signal line length and increasing wireability and yet exhibiting satisfactory solder joints.
A first general aspect of the present invention provides a method of filling at least one aperture in a substrate comprising: providing a substrate having a top surface and a bottom surface; providing at least one aperture in the substrate, the aperture extending from the top surface to the bottom surface; providing a filling structure having a first layer, a fill material over the first layer, and a mask over the fill material with at least one opening therethrough; placing the filling structure on the top surface of the substrate; and forcing the fill material through the at least one opening in the mask of the filling structure into the at least one aperture of the substrate.
A second general aspect of the present invention provides a method of forming a structure used to fill an at least one aperture in a substrate, comprising: providing a first layer; depositing a fill material over the first layer; and forming a mask over the fill material.
A third general aspect of the present invention provides a structure used to fill an at least one aperture within a semiconductor substrate, comprising: a first layer; a layer of fill material over the first layer; and a mask over the layer of fill material.
The foregoing and other features of the invention will be apparent from the following more particular description of the embodiments of the invention.